History Question?

Rene Descartes was a soldier. He was lying in a hospital bed with a bullet wound when he noticed a fly crawling on the ceiling. It occurred to him that the fly might follow an equation defining its position with respect to one wall, and another equation defining its position with respect to the other wall. That was the invention of the cartesian coordinate system, or what we call plotting. Before that, nobody had realized that they might draw a picture of an equation.